On Wed, 25 Jan 2023 at 12:34, Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> wrote: > > The runtime Power Management of CPU topology is not compatible with > PREEMPT_RT: > 1. Core cpuidle path disables IRQs. > 2. Core cpuidle calls cpuidle-psci. > 3. cpuidle-psci in __psci_enter_domain_idle_state() calls > pm_runtime_put_sync_suspend() and pm_runtime_get_sync() which use > spinlocks (which are sleeping on PREEMPT_RT). > > Deep sleep modes are not a priority of Realtime kernels because the > latencies might become unpredictable. On the other hand the PSCI CPU > idle power domain is a parent of other devices and power domain > controllers, thus it cannot be simply skipped (e.g. on Qualcomm SM8250). > > Disable the idle callbacks in cpuidle-psci and mark the domain as > always on. This is a trade-off between making PREEMPT_RT working and > still having a proper power domain hierarchy in the system. > > Cc: Adrien Thierry <athierry@xxxxxxxxxx> > Cc: Brian Masney <bmasney@xxxxxxxxxx> > Cc: linux-rt-users@xxxxxxxxxxxxxxx > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx> Kind regards Uffe > > --- > > Changes since v3: > 1. Rework - disable idle states, mark as always on (Ulf). > 2. Extend Kconfig warning (Ulf). > > Changes since v1: > 1. Re-work commit msg. > 2. Add note to Kconfig. > > Several other patches were dropped, as this is the only one actually > needed. It effectively stops PSCI cpuidle power domains from suspending > thus solving all other issues I experienced. > --- > drivers/cpuidle/Kconfig.arm | 8 ++++++++ > drivers/cpuidle/cpuidle-psci-domain.c | 7 +++++-- > drivers/cpuidle/cpuidle-psci.c | 3 +++ > 3 files changed, 16 insertions(+), 2 deletions(-) > > diff --git a/drivers/cpuidle/Kconfig.arm b/drivers/cpuidle/Kconfig.arm > index 747aa537389b..8deaa2e05206 100644 > --- a/drivers/cpuidle/Kconfig.arm > +++ b/drivers/cpuidle/Kconfig.arm > @@ -24,6 +24,14 @@ config ARM_PSCI_CPUIDLE > It provides an idle driver that is capable of detecting and > managing idle states through the PSCI firmware interface. > > + The driver has limitations when used with PREEMPT_RT: > + - If the idle states are described with the non-hierarchical layout, > + all idle states are still available. > + > + - If the idle states are described with the hierarchical layout, > + only the idle states defined per CPU are available, but not the ones > + being shared among a group of CPUs (aka cluster idle states). > + > config ARM_PSCI_CPUIDLE_DOMAIN > bool "PSCI CPU idle Domain" > depends on ARM_PSCI_CPUIDLE > diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c > index c80cf9ddabd8..6ad2954948a5 100644 > --- a/drivers/cpuidle/cpuidle-psci-domain.c > +++ b/drivers/cpuidle/cpuidle-psci-domain.c > @@ -64,8 +64,11 @@ static int psci_pd_init(struct device_node *np, bool use_osi) > > pd->flags |= GENPD_FLAG_IRQ_SAFE | GENPD_FLAG_CPU_DOMAIN; > > - /* Allow power off when OSI has been successfully enabled. */ > - if (use_osi) > + /* > + * Allow power off when OSI has been successfully enabled. > + * PREEMPT_RT is not yet ready to enter domain idle states. > + */ > + if (use_osi && !IS_ENABLED(CONFIG_PREEMPT_RT)) > pd->power_off = psci_pd_power_off; > else > pd->flags |= GENPD_FLAG_ALWAYS_ON; > diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c > index 312a34ef28dc..6de027f9f6f5 100644 > --- a/drivers/cpuidle/cpuidle-psci.c > +++ b/drivers/cpuidle/cpuidle-psci.c > @@ -222,6 +222,9 @@ static int psci_dt_cpu_init_topology(struct cpuidle_driver *drv, > if (!psci_has_osi_support()) > return 0; > > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) > + return 0; > + > data->dev = psci_dt_attach_cpu(cpu); > if (IS_ERR_OR_NULL(data->dev)) > return PTR_ERR_OR_ZERO(data->dev); > -- > 2.34.1 >
